Because of spiralling energy costs over recent years, much consideration has been given to means of reducing metal-to-metal friction in various mechanical devices where oil or grease lubrication is employed. The goal is to reduce energy consumption by lowering coefficients of friction between moving parts. To achieve lowered friction, the use of lubricants containing very finely divided polytetrafluoroethylene (PTFE) polymers, which are known to provide unusually low coefficients of friction, has been proposed. The rationale is that the dispersed polymer will form a film on moving metal surfaces under conditions of both boundry and hydrodynamic lubrication, thereby reducing frictional losses.
Reick U.S. Pat. No. 4,127,491 has described for the above purpose an oil dispersion of a relatively high molecular weight, fluorocarbon resin, which is prepared from a colloidal aqueous dispersion of the resin, using a variety of additives as neutralizing agents, wetting agents and dispersants. The dispersions used contain water which complicates the production process. Moreover, the presence of water is undesirable under operating conditions.
Lewis U.S. Pat. No. 3,234,758 has described a uniform dispersion of powdered PTFE in a hydrocarbon base lubricating grease. These dispersions are not stabilized against PTFE sedimentation, and they are adversely affected by high shear forces. Reick U.S. Pat. No. 3,933,656 describes a PTFE dispersion which is stabilized to prevent PTFE agglomeration but not sedimentation. Reick U.S. Pat. No. 3,879,302 describes an aqueous PTFE dispersion which suffers at high rates of shear and suffers from PTFE sedimentation. Similarly, the aqueous dispersions described in Reick's U.S. Pat. Nos. 4,224,173, 4,284,519, 4,284,518 and 3,194,762 are not stabilized to prevent PTFE sedimentation, and their performance under high shear forces suffers.
It would be advantageous from a cost standpoint, a major consideration in the use of this type of additive, to avoid the use of an aqueous dispersion of the fluorocarbon as a starting material, since this unduly complicates the manufacturing process. It would also be desirable to employ a single dispersant rather than the combination of neutralizing agents, wetting agents and dispersants which are conventionally present in aqueous dispersions. Furthermore, it would be desirable to obtain a dispersion which is not adversely affected by high rates of shear. It is especially important to have a dispersion which shows essentially no sedimentation of PTFE after long periods of ambient storage, since sedimented polymer is difficult to redisperse.